Summary The current TB multidrug therapy eliminates the majority of the M. tuberculosis (Mtb) bacteria in the first 2-3 weeks of treatment. The residual population (1%) after this period of time has become a night mare for TB eradication. To eliminate this 1% of drug tolerant bacteria the current multidrug treatment has to be continued for 9 month. Patient's well-being improves rapidly in the first weeks of treatment and many of them withdraw from the therapy. The latter has facilitated the emergence and expansion of multidrug-resistant strains of Mtb (MDR) and new TB cases caused by these strains are even more difficult to cure. The primary goal of this proposal is to more rapidly eradicate drug tolerant bacilli using immunotherapeutic approaches. We believe it is possible to enhance the capacity of the host (patient) to eliminate the bacilli via immune derived bactericidal mechanisms. Our preliminary studies indicate that delivery of naked small interfering RNA [siRNA] transcripts targeting the TGF1 cytokine reduces the pulmonary bacterial load of mice chronically infected with Mtb. Moreover, this effect is enhanced in the absence of the IL-10 cytokine. Here we want to explore if we can improve this therapeutic approach by delivering the siRNA via gold nanoparticles. Thus, novel polyvalent siRNA gold nanoparticle conjugates (siRNA-GNPs) will be used to silence expression of tgf1 or il10 transcripts in the lungs of mice with a chronic infection of Mtb. Thereafter we will test if silencing of mRNA for TGF1 and IL-10 can enhance clearance of drug tolerant bacilli. Our long term goal is to shorten therapy for TB and to treat chronic MDR-TB infections. The outcomes will be documented using comprehensive bacteriologic, immunologic, pathologic approaches now routine in our laboratory. We are uniquely equipped with state-of-the-art BSL-III research facilities and have assembled a team of highly experienced researchers with expertise in the fields of mycobacteria infection and RNA regulation in eukaryotic cells.